Digital multimedia content is becoming widely distributed through broadcast transmission, such as digital television signals, and interactive transmission, such as the Internet. The content may be still images, audio feeds, or video data streams. However, the enthusiasm for developing multimedia content has led to increasing difficulties in managing, accessing and identifying such a large volume of content. Furthermore, complexity and a lack of adequate indexing standards are problematic.
The Moving Picture Experts Group (MPEG) has promulgated a Multimedia Content Description Interface, commonly referred to as MPEG-7, to standardize the description of multimedia content when it is transmitted from a system that generates the content to a system that presents the content to a user. In contrast to preceding MPEG standards such as MPEG-1 and MPEG-2, which relate to coded representation of audio-visual content, MPEG-7 is directed toward representing information relating to content, and not the content itself. The MPEG-7 standard seeks to provide a rich set of standardized tools for describing multimedia content, with the objective of providing a single standard for creating interoperable, simple and flexible solutions for indexing, searching and retrieving multimedia content.
More specifically, MPEG-7 defines and standardizes a core set of “descriptors” for describing the various features of multimedia content; “description schemes” for describing relationships among the descriptors, the descriptors and other description schemes, and among description schemes; and a “description definition language” (DDL) for defining the description schemes and descriptors. The descriptions and description schemes for a particular type of multimedia content are encoded into a DDL-based schema. Each descriptor entry in the schema specifies the syntax and semantics of the corresponding feature. Each description scheme entry in the schema specifies the structure and semantics of the relationships among its children components.
For example, a standard movie includes scenes, shots within scenes, titles for scenes, and time, color, shape, motion, and audio for shots. The corresponding schema would contain descriptors that describe the features of the content, such as color, shape, motion, audio, title, etc., and one or more description schemes, e.g., a shot description scheme that relates the features of a shot, and a scene description scheme that relates the different shots in a scene and relates the title of the scene to the shots.
A description scheme can be represented by a graph in which each descriptor and nested description scheme corresponds to a node, with the relationships among the descriptors and description schemes corresponding to the edges of the graph. Working with the graphical representations instead of the description schemes themselves introduces an additional level of abstraction that can make searching for, and modification of, description schemes more efficient. However, the graphs are generally complex and creating valid and efficient graphs will be difficult for most users.